The invention relates to a method for calculating a consumption and/or remaining range of a motor vehicle with an energy storage system for a drive which acts on at least one wheel of the motor vehicle, and to a motor vehicle.
Motor vehicles with energy storage systems for their drives have, on the one hand, a remaining range which is dependent on the energy currently stored in the energy storage system, and have, on the other hand, a consumption lever when they travel a certain distance. For this reason, methods have been proposed, in particular for motor vehicles with navigation systems, for determining the remaining range and/or the consumption of a motor vehicle and informing a driver thereof using the navigation system. For example, a range can be displayed in a superimposed fashion by an area of a map representation of a navigation system determined from the furthest points which can be reached. For example, areas which can still be reached with the currently stored energy, and which can be reached without return, can be characterized in one color, and further areas which can be reached with a return to the present location can be characterized in a different color (figurative representation of a “fried egg” shape in which “yellow—return” and “white=can be reached” would mean).
In order to determine the remaining range of a motor vehicle it has been proposed to use algorithms which are also used to determine routes to a destination to be traveled on in a navigation system. In this context, what is referred to as the Dijkstra algorithm or a derivative of the Dijkstra algorithm is mostly used. The Dijkstra algorithm is based on ultimately moving through the map data from one branching possibility to another starting from the starting position or current position, wherein an optimum path to a destination can be determined by a cost function, frequently the fastest travel-through time. Dijkstra algorithms, which ultimately feel their way through the map material, are also suitable for calculation of the remaining range if the cost function is based on the consumed energy for the route section as costs. However, during the determination of the remaining range there is no specific destination since it is necessary to advance in all directions, and the process is aborted if the energy consumed along the route corresponds to the energy currently stored in the energy storage system or exceeds the energy. This means that an enormous computing time and an expenditure on calculation which is very great are necessary to determine a remaining range or just points which can still be reached.
In addition, the Dijkstra algorithm is extremely inaccurate for calculating remaining ranges, at least in the case of relatively large ranges, since the actual consumption also depends on the driving style, the ambient conditions, the traffic and the like. The inaccuracy of the Dijkstra algorithm ultimately increases at least quadratically with the energy which is still present, with the result that a relatively high level of uncertainty has to be expected.
It has been proposed to take into account, within the scope of the Dijkstra algorithm, only relatively large roads, for example freeways and, if appropriate, also federal highways, but then the furthest points which can be reached which are then obtained are only points where this type of road is also present. Roads of a low category which lead away from these freeways and could potentially be reached are then possibly represented as unreachable in the display.
An alternative algorithm is proposed in patent application DE 10 2010 051 546.9-53 which was published after the priority date of the present document and in which, instead of the map data of the Dijkstra algorithm, it is proposed to base said algorithm on area segments which are each assigned energy costs, if appropriate as a function of direction, which costs are required to pass through the respective area segment. For example relatively large area segments of this kind can be selected, for example of a size of 2 km×2 km. Consequently, “running through” the area segments results in total in a consumption level which the motor vehicle has over the route which is run through. The calculation can be made here in a fashion analogous to the Dijkstra algorithm, wherein ultimately expansion occurs from a first area segment, in which the motor vehicle is, for example, situated at the current time, to a second area segment, which adjoins the first area segment and to which the lowest energy costs of all the area segments adjoining the first area segment are assigned. In the next step, expansion then occurs from the first and second area segment to a third area segment which adjoins the first area segment and to which the lowest energy costs after the second area segment of all the area segments adjoining the first area segment are assigned, or which adjoins the second area segment if in total lower energy costs are assigned to the first, second and third area segments than are assigned in total to the first area segment and that area segment to which the lowest energy costs after the second area segment of all the area segments adjoining the first area segment are assigned. This method is continued iteratively for the next area segments. Alternatively or additionally, the area segments can be expanded in a star shape and/or recursively for the calculation of consumption and/or ranges. The calculation of consumption and/or ranges on an expansion path can be aborted if the total of the energy costs of the area segments reaches or exceeds a predefined quantity of energy, in particular the quantity of energy currently stored in the energy storage system. This algorithm can be carried out with a significantly lower amount of expenditure on calculation than the Dijkstra algorithm based on the road network, with the result that a saving in terms of resources and time can be achieved. Although the algorithm is more heuristic than the Dijkstra algorithm, this is less relevant in particular in the case of large ranges since the influences which cannot be covered by the algorithm, and which have already been discussed above, give rise to a certain degree of inaccuracy in any case.
DE 10 2008 037 262 A1 discloses a method for outputting a determined remaining range of a refueling of a motor vehicle in a visual output of a navigation system of the motor vehicle. In this context, two possible ways of displaying the range are disclosed, specifically as a polygonal line or a circle. When the polygonal line is determined, inter alia roads and localities which can be traveled along or through by the vehicle are taken into account, wherein the range along a cross-country road is larger than when traveling through a town. The polygonal line can be displayed as a function of the filling level of the fuel tank. In this context, a sharpness of the polygonal line is selected as the fuel tank content decreases owing to more precise determination of the range.
EP 2 172 740 A1 relates to a map display device, wherein it is stated that it is difficult for a user to determine how long he has to charge a battery until a desired remaining range is achieved if he can only input a charging time in order to calculate this. As a solution it is proposed in said document that a range be determined for a plurality of charging times and that these ranges be displayed simultaneously. It is detected that in the case of a relatively large range a relatively large error occurs, with the result that a reduction in the determined range is to take place.